Once a well has been drilled into an underground formation to obtain fluids contained in the underground formation, it is necessary to establish a system for removal of these fluids from the formation through the well bore. Typically the fluids enter the passages or tunnels which are formed in the formation. As the passages or tunnels are positioned to be near perforations formed in the casing which lines the well bore, the fluids flow through these perforations into the production piping through a screen formed in the production piping. Following the completion of a well, the fluids flow out the top of the well through one or more openings formed in the wall of an isolation pipe string assembly.
Wells drilled in sandy formations present distinct problems for well operators. Not only does the sand from the formation clog equipment, its abrasive nature quickly damages the equipment used to conduct fluids out of the well bore. Further, when sand is removed from the formation from which fluids are obtained, the formation surrounding the well bore may actually collapse and thus prevent further extraction of fluids from the well.
The necessity for and the systems typically used to control sand in wells is explained in an article entitled "Sand Control: Why and How?" which was published in Oil Field Review 4, No. 4 (October 1992) at pages 41-53.
To assure the continuous production of fluids through the well bore it is necessary to stabilize the passages or tunnels formed in the sandy formation through which the fluids must pass before being extracted through the well bore. Such stabilization is called well completion. Several different methods are typically used to stabilize the passages or tunnels which emanate outwardly from the well bore. The most popular of these well completion methods is known as gravel packing.
In the gravel packing method of completion of a well, gravel and a carrier or completion fluid are injected into the well in the form of a slurry. The slurry is guided into position near that portion of the formation through which fluid flow using a gravel packer assembly. The solid portion of the gravel slurry collects in the tunnels formed in the sandy formation through which the fluids pass and it also collects in the annular space between the interior wall of the casing which lines the well bore and the exterior wall of the production piping which is passed through the casing. This collection of solid gravel both stabilizes the tunnels formed in the sandy formation exterior to the well bore and it also acts as a filter to dramatically reduce the amount of sand which flows into the production piping.
The carrier fluid, or the completion fluid, which is used to create the gravel slurry to move the solid gravel into the well bore and into the tunnels which emanate outwardly from the well bore either leaks off into the sandy formation or is allowed to flow back into the well. In many situations well operators desire to prevent the flow of completion fluids through the sand control production screen. Accordingly, there is a need for a downhole tool which will prevent undesired fluids from flowing through the sand control production screen.
A didatic description of a system for the placement of a gravel pack assembly in a well appears in U.S. Pat. No. 4,858,690. This patent describes the placement of a gravel pack or assembly in a sub-sea well.
U.S. Pat. Nos. 5,579,844 and 5,609,204 describe systems for the zonal isolation of wells from the flow of completion fluids. The construction of the tools described in these two patents is complex and accordingly these zonal isolation tools are expensive and difficult to operate.
Therefore a need remains in the art to provide an inexpensive zone isolation system for use with a gravel packer assembly which has a minimum number of parts and is both reliable and easy to operate.